Let us examine the form of the verb in question.
突っ走る is the 終止形 (Dictionary form) Or the form you would normally use for present/future tense.
突っ走り is the 連用形 (Verb continuative form)
One of the uses of a verb in 連用形 is to form verbal compounds:
Consider these in isolation:
Now consider the compound from their combination:
- 着物{きもの} meaning "kimono" or literally as "a thing you wear" (着 is the 連用形 of 着る)
Now let's examine つっぱしり元太郎:
Consider them in isolation:
Put them together to form:
- つっぱしり元太郎 - "(the) Gentarou (who) runs swiftly"
Now let's compare つっぱしる元太郎 with つっぱしり元太郎.
Using 連用形 to modify the noun makes it an (intrinsic) attribute of the noun. Using the plain form(連体形) to modify the noun describes the noun in terms of what it is currently doing(being) or will do(be).
Tidbit on 終止形 and 連体形:
手紙はペンで書く (Write a letter with a pen)
書く is in 終止形 or "sentence ending form" or "predicative form"
ペンで書く手紙 (A pen-written letter)
書く is in 連体形 or "attributive form"
There might be some confusion because now apparently the "attributive form" does not in fact give the noun the attribute! Actually what it does is it attributes the action to the noun, which is so very different from describing it with an intrinsic attribute.
Compare with 書き手紙. That would mean "the letter that writes" which does not make sense under most contexts.
連用形form of突っ走るwas used (as opposed to the dictionary (or some other) form.) What specifically does the連用形of a verb preceding a noun (in this case a name) mean? Do you have any good resources on the subject? :) – Miguel Nov 09 '11 at 06:30